dc.description.abstract |
Glacierised basins are significant sources of
sediments generated by glacial retreat. In Himalaya, most of the
glaciers are covered by thick debris, especially in the ablation
zone. Supraglacial debris cover might play an important role for
sediment budget of the glaciated area or for the ablation of ice
masses mantled in debris. The glacier system includes
sedimentation from different parts of the glacier such as the
accumulation zone, ablation zone, snout and the lateral
moraines, whereas bedrock system deals with glacier bottom ice
and bedrock. During summer season, proglacial meltwater
carries considerable amount of suspended sediment. The
deglaciated area provides a ready source of sediment during
monsoon. Estimation of suspended sediment transfer from
glacierised basins is very important in reservoir planning for
hydropower projects in Himalaya. Assessment of these
sediments transported by the melt stream is important because
it has direct influence on the capacity of the reservoirs.
Suspended sediment yields in particular are viewed as a
sensitive parameter of environmental change, since suspended
sediment is broadly supply-controlled, while bed load is broadly
hydraulically controlled; therefore, it is expected that suspended
sediment fluxes are more responsive than bed load fluxes to
climate-driven environmental change, other factors being equal.
An assessment of suspended sediment concentration (SSC), load,
yield and erosion rate has been undertaken for the Gangotri
Glacier drainage basin (nearly 50% glaciated) located in the
Garhwal Himalayas. . The proglacial melt water stream, known
as Bhagirathi River, emerges out from the snout of the Gangotri
Glacier at an elevation of 4000 m. The Gangotri Glacier system
most commonly known as Gangotri Glacier, is a cluster of many
glaciers comprising of main Gangotri Glacier (length: 30.20 km;
width: 0.20 - 2.35 km; area: 86.32 km2) as trunk part of the
system. The flow data was collected from field observations near
the snout of the glacier. To determine the mean suspended
sediment concentration, load, yield and particle size in the
Gangotri Glacier melt stream, two water samples at 0830 and
1730 hours were directly scooped from the channel at the
gauging site in a cleaned polyethylene bottle (500 ml). Data
were collected for four ablation seasons (2011–2013). Mean
monthly SSCs, for May, June, July, August and September
during the study period was 1,435, 1,677, 2,086, 1,499 and 528
ppm, respectively, indicating highest SSC in July, followed by
August. For the entire melt season, the mean daily SSC was
computed to be 1,445 ppm. Similar trends were also found for
the sediment load and about 67% of the total suspended
sediment load of the melt period was transported during the
months of July and August. There is a wide variation in the
daily concentration of suspended sediment and SSLs. Both
sediment concentration and load were found to be highest in the
monsoon months and nearly two-thirds of the total sediment
load was transported in these 2 months. |
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